compressibility

[LSimons]

Though this may have been discussed earlier, I would like to suggest that a mandolin's "compressibility" might serve as an objective measure of the mandolin's acoustic properties. When a string breaks or when it is removed from an in-tune instrument, the other strings naturally sharpen as a result of the instrument uncompressing. The more the remaining 7 strings sharpen is a measure of the instruments compressibility. With nearly everyone has an electronic tuner it should be possible to get a data base of this parameter and maybe there might be some relationship to tone or volume. I have recently be lucky enough to get two pretty nice mandolins that seem to be much more "compressible" than a cheaper mandolin I once had.

[HoGo]

This sound like a variation on the deflection tuning, but with whole body of a mandolin. I don't think this will be objective. The neck and peghead thickness are in the equation and they have not much to do with tone quality. You could probably measure loudness of the instrument. The overall amount of wood left in the body-blocks, sides, plates and neck and the stiffness of the wood is main factor in the "compressibility". You may have mandolin with too thick back and too thin top that will have same "compressibility" as another that has thick top and thin back... The quality of tone of the two will be radically diferent.

[sunburst]

The neck and peghead thickness are in the equation and they have not much to do with tone quality.
I wonder how much this does have to do with tone quality.
I don't know how one would measure and then relate the measurements to sound or tone, but I suspect thickness and stiffness of the neck/peghead may influence tone.

I understand that some classical guitar builders string up thier guitars while still in construction and can hear the guitar get louder as the neck is cut thinner.

Back when I used to work for a b@^jo manufacturer, I could hear, but not see the new banjos as they were strung up and played for the first time. I had about 70% accuracy being able to tell what kind of wood the neck was from the tone of the instrument. Since a banjo is a bolt-together instrument, it's relatively easy to change necks and hear the difference. Mandolins would be hard to experiment with, but why wouldnt different neck characteristics contribute to different sounds?

As an afterthought it occurs to me that a Rigel mandolin, with it's bolt on neck could serve as a model for experimentation. Perhaps Pete has tried some experiments. Anyone know?

[HoGo]

IMHO on mandolin the neck is rather short and stiff comparing to b@ni0 or giutar. The influence of thinning the neck of a mandolin would be more in volume department(because you reduce weight) than in the tone timbre.
The peghead thickness counts for this "compressibility" when it is quite thin and bends a tiny bit when strung up. The species of wood doesn't count that much either as maple is used on most mandolins.
And yes, I agree that neck wood has big effect on tone of the b@ni0 or other long & thin necked instruments.
I've thinned a neck of one of my mandolins considerably (almost 3/16" in the 7th fret area) and changed profile from round to parabolic and didn't hear a noticeable difference in tone.

[LSimons]

I claim it is objective in that the extent of sharpening of the remaining strings after loosening (or breaking) one string is not a matter of opinion, but a measurable physical property. I believe that whole mandolin structure, and especially the sound chamber, is deformed by the tension of 8 strings, and that removal of one (or more) will relieve some of this tension, allowing the mando will return toward its zero tension structure.

I would like to think that a mandolin's "compressibility" might be useful, but if not it remains is measurable.

[sunburst]

LSimons,

I agree that the amount of "release" following a broken string is measurable and, in general, indicates how stiff the structure of a mandolin is. There might be something to be learned from a data base.

I also agree with HoGo in that you would be measuring many different things that contribute to the stiffness of the structure of the mandolin at once with no good way to know specifically where the "compressability" is coming from or in what proportions it comes from different aspects of the structure.

[HoGo]

Sunburst, you hit the nail on its head. It is not possible to compress such a complex information as tone quality into one single number without losing most of it.

[Big Joe]

I'm not sure how that test would really translate to anything functional, but it may be worth the experiment. As to neck and peghead effects on tone it can be substantial. Our Bush model has a larger neck and peghead than our other F5's and there is a noticeable tone difference. The only difference is the neck so there are no other variables to consider. The extra mass does affect volume as well, but it surely affects tone.

One other thought. The compression of the instrument will be greater with a thinner top or back plate. While that may be somewhat subjective, there is a point where tone begins to fall off in relation to thickness. If it is too thick or too thin it will cause a difference in the tonal properties. Not all those differences are considered desireable. Secondly, each piece of wood...even within a species...is different and will have differing acoustic properties. Therefore, one instrument made with the exact same materials at the exact same specs will have a different deflection because of the differences in the wood. Then add differing glues, differing neck joints, differing bridge fits, differing nuts, differing tuners, tailpieces, strings, bracings that are available and they all have an effect on the total amount of compression or deflection. Therefore compression and deflection become less scientific. Too many variables to control in any reasonable real world situation. Just some thoughts.

[peter.coombe]

To those that don't believe that the neck makes a difference, I suggest you read some of the violin literature. There is a neck mode in the violin that does affect tone, and the same neck mode is also in mandolins. I have found that if you tune the neck mode close to the resonant frequency of the soundbox, you will get increased ring and sustain.

[HoGo]

Big Joe, I heard Charlie D. say somwhere that the Bush Model has also the top thinned a bit more around the f-holes...

Peter, thanks for the insight. I agree with you, but what I found in my own mandolin there was no change in the overall tone-timbre it still sounded like tha same mandolin. I cannot speak for the ring and sustain as I changed stings gauge at the same time. Violin neck and the whole body are much more elastic (you can even feel the elasticity when you try to bend the violin), the effect of a neck tuning on a violin will be bigger than on mandolin. But the more variables, even the smallest ones, you can control, the better control over the tone of finished instrument you have.

[LSimons]

I have just done a rather crude measure of the "compressibility" on my two mandos by carefully tuning to std pitch, then releasing tension on one of E strings, then rechecking the tuning. I found an average increase in pitch of the remaining 7 strings to be 16 and 18 cents on mando A and B respectively. I don't have a good frequency counter so am not that confident of these results, but the ease of making this measurement can be noted. I make no claim that this measurement will be useful for anything, but it is essentially free and easy. Who knows what a large data base of these measurements might lead? Big Joe, what do your Master models (I'm dying to have one) measure, or what about the Loars?

[HoGo]

LSimons, What we all forgot is that the gauge and material of strings will have also grat effect on this.

[sunburst]

LSimons, I checked the two mandolins that I have here.
Both have .011 in E strings, both are Hamlett F style, both have rock maple (stiff) necks, one has a Sitka top and the other has a Red spruce top.
Results: With one E string completely loosened, the other E on both mandolins sharpened 20 cents. The G strings didn't change significantly.

[Flowerpot]

Hmmm sunburst, would the fact that the G didn't change much imply that most of your "compression" is coming from the top? (If the neck were flexing, I'd think that all the strings would be affected, whereas the top can skew from treble to bass side.) It would be consistent with your stiff neck construction. I wonder if measuring E and G strings like you did might tend to tell a little bit about where the compression is coming from.

Incidently, my gut would tell me that having most of the flex coming from the top, rather than from other areas, would be a desirable thing for volume/tone.

[sunburst]

Mark, I suspect likewise. It would be somewhat similar to a bicycle frame in that the stiffer the frame, the more of your energy gets converted into work. In the case of the bike, the work goes on mostly at the back wheel, in the case of the mandolin the work goes on mostly in the body.

Of coarse, there are other things to consider. The neck resonance mentioned earlier in the "tap tuning" thread as well as "restoring forces" which, I suspect, might be related to the neck resonance.

[peter.coombe]

I am very sceptical about whether static measurements such as measuring "compressibility" (actually one measure of stiffness) is really of much use at all. A music instrument is a non linear DYNAMIC system where all the parts interact and contribute their various properties to produce tone. One measure of stiffness is a very small part of the whole equation.

[Bluemando]

This is a interesting thread. I noticed (with the mandolins that I have played, and the one that i have built,) that the thicker the headstock, the more sustain I tend to have.
With that said, would'nt sustain, be an after-product of tone and volume combined, and therefor any change in any aspect of building would change tone, volume, sustain, etc. (just a thought)

[sunburst]

Bluemando, I read an article somewhere (it's been too many years to remember where the article was) about restoring forces. I mentioned restoring forces in an earlier post in this thread.
Imagine a string drawn tight between two walls of concrete. If you pluck the string, in will vibrate until it stops. Now imagine the same string, but the walls are wood. The article suggested that if you now pluck the string, it will vibrate longer because the wood will resonate sympathetically and restore the vibrations, hence restoring forces.
With that as background, the article went on to describe a simple experiment. Put a C-clamp, padded of coarse, on the head stock ond another on the tailblock of an instrument and observe the added sustain derived from the added mass at the extreem ends of the instrument.
The conclusion was, as you say, a thicker headstock will contribute to greater sustain, not so much because of the thickness as because of the mass.

I suspect this is only one variable and stiffness has an affect too. I also think that loudness is sometimes diminished in search of sustain. It's all food for thought tho.